... of the flow. *U. S. Army Aeromechanics Laboratory, Moffett Field, CA 94035 .... The distribution of Reynolds stress u'v' is altered under oscilla- tory conditions ...
NOTICE
THIS DOCUMENT HAS BEEN REPRODUCED FROM MICROFICHE. ALTHOUGH IT IS RECOGNIZED THAT CERTAIN PORTIONS ARE ILLEGIBLE, IT IS BEING RELEASED IN THE INTEREST OF MAKING AVAILABLE AS MUCH INFORMATION AS POSSIBLE
t ti
NASA Technical Memorandum 81304
USAAVRAUCOM TR 81-B-17
1
4
(NASA -TfI- 81304) llYNA!4 1C bEdAYiUR OF AN UhSTkADY i&UjuLENT uLUbLAi:Y LAYia (NASA) 14 p HC A02/ME AU1 CSCL 20D
N61-2b392
U.UC a z li2/34 27U22
Dynamic Behavior of an Unsteady Turbulent Boundary Layer P. G. Parikh, W. C. Reynolds, R. Jayaraman and L. W. Carr
y'JJ,Jj a
July
1981
RVGA
National Aeronautics and Space Administration
Ames Research Center Moffett Feld California 94035
United States Army Aviation Research and Development Command
F
7
NASA Technical Memorandum 81304
USAAVRAOCOM TR
Dynamic Behavior of an Unsteady Turbulent Boundary Layer P. G. Parikh, W. C. Reynolds, R. Jayaraman,
Department of Mechanical Engineering Stanford University, Stanford, California
L. W. Carr, Aeromechanics Laboratory AV RADCOM Research and Technology Laboratories Ames Research Center, Moffett Field, California
NMA Nation,il AerunautlCS and Space AdrT)InIStI.Oon
United States Army, S` Aviation Researc ri and Development!'^ Commend
ur
eutjt% %o.- tt i
i
DYNAMIC BEHAVIOR OF AN UNSTEADY TURBULENT BOUNDARY LAYER BY P.G. PARIKH,W.C. REYNOLDS, R. JAYARAMAN, Department of Mechanical Engineering Stanford University AND L. W. CARR U.S. Army Aeromechanics Laboratory Moffett Field, Ca
Presented at the IUTAM Symposium on UNSTEADY TURBULENT SHEAR FLOWS 5-8 May,1981 TOULOUSE, FRANCE
'RECEt)iNG P AGE BUNK NOT FILME3
-iii-
^^^
DYNAMIC BEHAVIOR OF AN UNSTEADY TURBULENT BOUNDARY
LAYER
P. C. Parikh, W. C. Reynolds, R. Jayaraman, and L. W. Carr* Department of Mechanical Engineering, Stanford University Stanford, California 94305 Summary
This paper reports experiments on an unsteady turbulent boundary layer. The upstream portion of the flow is steady (in the mean). In the downstream region, the boundary layer saes a linearly decreasing free-stream velocity. This velocity gradient oscillates in time, at frequencies ranging from zero to approximately the bursting frequency. Considerable detail is reported for a low-amplitude case, and preliminary results are given for a higher amplitude sufficient to produce some reverse flow. For the small amplitude, the mean velocity and mean turbulence intensity profiles are unaffected by the oscillations. The amplitude of the periodic velocity component, although as such as 70Z greater than that in the free stream for very low frequencies, becomes equal to that in the free stream at higher frequencies. At high frequencies, both the boundary layer thickness and tLe Raynolds stress distribution across the boundary layer become frozen. The behavior at larger amplitude is quite similar. Most importantly, at sufficiently high frequencies the boundary layer thickness remains frozen at its mean value over the oscillation cycle, even though flow reverses near the wall during a part of the cycle. Introduction The objectives of the Stanford Unsteady Turbulent Boundary Layer Program are: to develop a fundamental understanding of such flows, to provide a definitive data base which can be used to guide turbulence model development, and to provide test cases which can be used by computors for comparison with predictions. Due to space limitations, work of other investigators will not be summarized here, except to note that all the previous experiments are characterized by unsteady flow at the inlet to the unsteady region. For a comparison of the present experimental parameter range with those of other investigations, see Reference 1. The distinctive feature of the present experiments is that the boundary layer at the inlet to the unsteady region is a standard, steady, flat-plate turbulent boundary layer. It is then subjected to controlled oscillations of the free stream. :his feature is especially important from the point of view of a computor, who nee4a precise specification of boundary conditions for computation of the flow.
* U. S. Army Aeromechanics Laboratory, Moffett Field, CA 94035
roe-Stream Boundary Condition of the Present Experiment The desired frerstroom velocity u„(x,t)
in the water tunnel built
or this wort is shown in Fig. 1. u. remains steady and uniforc for the first two motors of boundary layer development., It then-decreases Usarly in the test section; the magnitude of the velocity at-adi% varies inusoidally from zero to a maxinum value during the oscillation cycle. he mean free-stream velocity distribution in the test section is thus inearly decreasing and corresponds to the distribution at the cycle phase ngle of 90', while the amplitude of imposed free-straam oscillations rows linearly in the streamwise direction, starting at zero at the otrance to a maximum value of a 0 at the exit. Hance,
u-(x,t)
• U.
x < x0
'o a "X -,
u,.
to
-
-
L° Cl - cosmt],
%
